Gulf of Maine Seasonal Sea Surface Temperature Update

Seasonal Patterns in Sea Surface Temperatures

Author

Adam Kemberling

Published

April 12, 2023

About the Updates:

Over the past decade, scientists at the Gulf of Maine Research Institute have led a body of research that highlights the rapid pace of warming in the Gulf of Maine. To keep you informed, we share seasonal updates about conditions in the Gulf of Maine.

New in 2023: Moving the Climatological Reference Period

In the field of climate science, 30-year time periods are a standard measure for a “climatological reference period”. Such a timescale adequately captures the natural inter-annual variability of the Earth system to enable rigorous statistical analysis of trends in environmental conditions. This is particularly relevant when presenting statistics such as temperature “anomalies”—or deviations from these 30-year climatological averages. To date, when we present temperature anomaly data in our seasonal and annual warming updates, we have used a climatological reference period of 1982-2011. In part, this is motivated by the fact that reliable satellite data for sea surface temperatures (SST) in the Gulf of Maine became available in 1982 (and 30 years hence brought us to 2011). Beginning with this winter 2022-23 Gulf of Maine warming report, we are using a new 30-year climatological reference period, 1991-2020, reflecting the fact that an additional decade’s worth of data has been collected, enabling us to update our baseline reference period. This change is consistent with best practices used by the international science community. For more information on 30-year climatological (or baseline) reference periods, the motivation for, and implications of updating it to 1991-2020, visit the U.S. “Climate Normals” database or this explainer from the National Oceanic and Atmospheric Administration (NOAA).

For the Gulf of Maine, the update of the seasonal climatology can be seen most clearly in February and March as temperatures no longer reach peak-lows. As well as in August and September where temperatures are setting new records. SST is higher throughout the year with this new climatology, and this will be reflected in all figures and tables as anomalies from this CRP will be lowered. However, underlying trends will remain unchanged, as will warming rates.

Learn more about how scientists study climate, and the details of this transition, in our marine heatwaves technical report.

Note About the Data: The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.

The Gulf of Maine Region

For analyses like these, it is important to be clear about the spatial extent that “defines” the Gulf of Maine (Figure 1), as different borders could produce different results. The spatial domain we use as the “Gulf of Maine” is displayed below. This area is consistent with previous seasonal and annual Gulf of Mainereports GMRI has produced.

An overhead view of the Gulf of Maine region. Landmasses and political boundaries for the United States and Canada are displayed. A blue dotted line outlining a box with a transparent blue fill is shown to demark where satellite data for the analysis has been used.

Figure 1: Spatial domain used for Gulf of Maine SST analyses. Deeper blues indicate deeper water depths.

Season Highlights

For this seasonal report we present an analysis of SST for winter 2022-23 (December 1st - February 28th). During this season, the average SST for the Gulf of Maine was 47.64°F, making it the new hottest winter on record for the period of 1982-2023 — the period over which the satellite data used are available.

Weekly Temperatures

In (Table 1), we highlight how the SST for each week this winter compares to the 30-year CRP period (i.e., climatological averages from 1991 through 2020) for the area shown in Figure 1.

The observed SST, long-term average SST trends, and SST anomalies (i.e., departures from the long-term average SST) are shown. Departures from the long-term average hovered around 3°F above normal with a few weeks punctuated by anomalies in excess of 4F in early- to mid-December and from late January through most of February with the last of 2022 and first week of 2023 experiencing temperatures closest to the long-term average.

Table 1: Observed, climatological average, and deviation from the climatological average (i.e., temperature anomaly) for SST at a weekly resolution in the Gulf of Maine during winter 2022.
Weekly Sea Surface Temperatures - Winter
(December 1, 2022 - February 28th, 2023)
One-Week Period Observed Temperature Climatological Average Temperature Anomaly
°F °C °F °C °F °C
Dec 01 - Dec 03 52.40 11.40 49.30 9.64 3.10 1.72
Dec 04 - Dec 10 53.00 11.70 48.70 9.25 4.33 2.41
Dec 11 - Dec 17 52.50 11.40 47.70 8.72 4.83 2.68
Dec 18 - Dec 24 50.60 10.30 46.70 8.19 3.88 2.15
Dec 25 - Dec 31 47.80 8.77 45.80 7.68 1.96 1.09
Jan 01 - Jan 07 46.40 7.99 44.90 7.18 1.45 0.81
Jan 08 - Jan 14 46.50 8.04 44.10 6.71 2.40 1.34
Jan 15 - Jan 21 46.60 8.10 43.30 6.25 3.33 1.85
Jan 22 - Jan 28 46.70 8.14 42.50 5.85 4.13 2.29
Jan 29 - Feb 04 46.10 7.86 41.90 5.48 4.28 2.38
Feb 05 - Feb 11 44.70 7.05 41.30 5.16 3.40 1.89
Feb 12 - Feb 18 45.20 7.31 40.80 4.90 4.34 2.41
Feb 19 - Feb 25 45.20 7.34 40.40 4.68 4.78 2.65
Feb 26 - Feb 28 43.80 6.58 40.20 4.57 3.63 2.02
Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data.
Climatological Reference Period: 1991-2020.

Monthly Statistics

Table 2 shows monthly average SST for winter 2022-23, where we see each month was nearly 3°F or more above the 1991-2020 CRP. February showed the largest deviation from the long-term climatological average, with an average SST anomaly of 4.11°F.

Table 2: Observed, climatological average, and deviation from the climatological average (i.e., temperature anomaly) for SST at a monthly resolution in the Gulf of Maine during spring 2022 (defined as March 1 through May 31).
Month Monthly SST Ranking Observed Temperature Climatological Average Temperature Anomaly Temperature Progression
°F °C °F °C °F °C High/Low °F
Dec 1 51.10 10.60 47.40 8.57 3.69 2.05 46.9
Jan 3 46.50 8.07 43.50 6.41 2.99 1.66 46.6
Feb 1 45.00 7.23 40.90 4.95 4.11 2.28 43.7
Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data.
Climatological Reference Period: 1991-2020.

How Does this Winter Compare?

2023 2022-23 is the new warmest winter season observed in the Gulf of Maine during the 41 years we have satellite data to analyze. The top 5 warmest winter seasons have all occurred in the last decade.

Figure 3: A ranking of the 5 warmest winter seasons for the Gulf of Maine in the satellite record (1982-2023). 2022-23 was the warmest winter on record; the past three winters were each the warmest until that point; and the five warmest winters have all occurred since 2015.

Marine Heatwave Conditions

The most commonly used definition of a “marine heatwave” (MHW) is when daily average SSTs exceeded the 90th percentile of a climatological (i.e., 30-year) average for at least 5 consecutive days. Gaps of 2 days or less in this threshold do not constitute a break in the MHW event.

Using this broadly accepted definition, the Gulf of Maine has experienced MHW conditions for 82% of this winter. A 16 day period over the New-Year’s transition (Dec 27th - January 11th) were the only dates where SST was below the threshold of a MHW.

Figure 4: A timeseries of marine heatwave (MHW) conditions in the Gulf of Maine extending from December 1, 2022 through February 28, 2023. Black lines represent the long-term (i.e., 1991 – 2020) average SST, the 10th percentile, and 90th percentile for a given day in the Gulf of Maine are labelled to indicate climatological reference points; a solid line (red for marine heatwave or blue for a non-event) indicate the observed SST this year; red and blue shading illustrates how far the observed SST falls from the climatological mean.

Presenting SST conditions in terms of anomalies (Figure 5) as opposed to absolute values (Figure 4) illustrates in greater detail the magnitude of MHW conditions throughout the winter. The most extreme daily SST anomalies occurred in December, with temperatures exceeding 5°F above the climatological average. Temperatures fell closer to the CRP average towards the end of December, before rising to the +3 to +4°F range for the second half of January and through February.

Figure 5: A timeseries of daily average SST anomalies in the Gulf of Maine (solid red line) compared to marine heatwave (MHW) conditions (dashed black line) in the Gulf of Maine for the period December 1, 2022 through February 28, 2023.

Heatmap of Temperature Anomalies and Heatwave Events

Looking at the full record of daily SST anomalies in the Gulf of Maine (Figure 6), the distinct thermal regime shift beginning around 2010 is evident. Indeed, since 2012, the Gulf of Maine has experienced far more persistent MHW conditions (indicated by solid black lines) than at any other point in the satellite record.

Figure 6: Heat map of daily SST anomalies from the beginning of 1982 through Winter 2022-23. Not only do more large warm anomalies (darker reds) appear more frequently in recent years, but the frequency, duration, and intensity of marine heatwave events (black lines) in the Gulf of Maine has become more pronounced in the past decade.

The Visual Impact of a New Climate Reference Period

If we compare our new heatmap figure (Figure 6) to what it was previously, the transition to a new climatological reference period can be seen more clearly. Using the slider below, we can reveal that the transition has removed many of the heatwave events prior to 2012. The new CRP has also impacted how severe the thermal stress of the last decade appears. This period is still clearly distinct in terms of higher temperatures and the frequency of MHW events, but the MHW record has been changed.

Figure 7: ?(caption)

Figure 8: ?(caption)

Spatial Distribution of Seasonal Anomalies

From a spatial perspective, the Gulf of Maine and (most) surrounding areas experienced above average SSTs during winter 2022-23, but the warmest patches were to the south and east of Georges Bank, mostly outside the domain analyzed in preceding sections. The highest seasonally averaged anomaly of any location above was 11.41°F.

Figure 9: Map of average SST anomalies for each grid cell in the satellite record for winter 2022-23. The box outlined by the black dashed line denotes the region of study for the analysis (see Figure 1). Darker red regions indicate warmer anomalies.

Monthly Temperature Anomalies

Average monthly SST anomalies are shown in Figure 10. The warmest anomalies were observed in December and February and were largely confined to areas just beyond the region of study (i.e, beyond the continental shelf where the Gulf Stream and Labrador Current have significantly more influence on oceanic conditions).

Figure 10: This series of maps shows the average monthly SST anomaly for December 2022, January 2023, and February 2023. The box outlined by the black dashed line denotes the region of study for the analysis. Darker red regions indicate warmer anomalies.

A Note on Data Sources:

NOAA_ERSST_V5 data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.ersst.v5.html.

NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html.

Citing This Work

If you would like to cite this report, please use:

Gulf of Maine Research Institute. 2022. Gulf of Maine Warming Update: Winter 2023

 

A work by Adam A. Kemberling

Akemberling@gmri.org